1. Field of the Invention
This invention relates generally to electron discharge devices and is concerned more particularly with a cathode support structure for such devices.
2. Discussion of the Prior Art
An electron discharge device generally comprises an evacuated envelope having therein an electron emitting cathode disposed to beam electrons toward a spaced anode collector electrode. The cathode may be of the indirectly heated type including a cathode cup having an electrically heated filament extended insulatingly into the open end thereof. The cathode cup usually is made of suitable metallic material, such as nickel, for example, and has a closed end provided with an exterior coating of low work function material which emits electrons copiously when heated. The cylindrical wall of the cup may be provided with a circumferential pair of axially spaced ripples which extend radially outward of the cup. Disposed between the ripples may be an inner peripheral portion of a closely encircling support ring which is made of suitable dielectric material, such as ceramic, for example.
When the ripples are formed in the cylindrical wall of the cup, they bear tightly against respective opposing flat surfaces of the encircling support ring, thereby fixing the cup in predetermined spaced relationship with respect to the anode collector electrode. However, when the cathode cup is heated to an unusually high temperature, such as during "hot-shot" treatment, for example, the metallic material of the cup expands thermally at a faster rate than the closely encircling support ring. As a result, the cylindrical wall of the cathode cup is pressed annularly against the inner periphery of the support ring and receives a resulting circumferential crimp which extends radially inward of the cup. Accordingly, when the cathode is cooled to room temperature, the circumferential crimp is permanently set in the cylindrical wall of the cathode cup; and the inner peripheral portion of the support ring is no longer locked tightly between the circumferential ripples in the cylindrical wall of the cup. Consequently, when the tube is operated under vibrational or shock conditions, the loosened cathode cup is permitted to move relative to the other elements of the tube. Thus, the intensity of electrons beamed to the collector electrode may vary erratically and may effect the accuracy of an informational signal being amplified or displayed by the tube.
Therefore, it is advantageous and desirable to provide an electron discharge device with a cathode support structure which will maintain the cathode in fixed positional relationship with other electrodes of the device.